In recent years, accompanied by downsizing and high densification of semiconductor device, as a method of mounting semiconductor chip on a circuit substrate, flip chip assembly (direct chip attach assembly) has drawn attention and has been spreading widely. In the flip chip assembly, as a method of keeping connection reliability of bonding portion, it is adopted as a general method, after bonding bump electrodes built on the semiconductor chip to pad electrodes of circuit substrate, to inject a liquid encapsulant into a gap between the semiconductor chip and the circuit substrate. However, for making semiconductor device small and light, due to increased number of bump electrodes built on the semiconductor chip and low profiling requirement of the bump electrode, there appeared some cases in which it is impossible to adopt conventional method to inject the liquid encapsulant into a gap between the semiconductor chip and the circuit substrate sufficiently to keep connection reliability of the bonding portion. To this problem, it has become being adopted that the semiconductor chip and the circuit substrate are bonded after coating a liquid adhesive called as underfill material to the semiconductor chip with circuit substrate or bump electrode by a method such as dispenser or screen printing. However, since it was difficult to uniformly coat the liquid adhesive in micro area, there were problems, due to flowing out of the liquid adhesive, that such as contamination of the circuit substrate or the semiconductor chip, expansion of assembling area and existence of unsealed portions (see Patent reference 1).
In order to solve this problem, a method of simultaneously carrying out an electrical bonding and resin sealing by, after laminating an adhesive composition for semiconductor of a predetermined thickness to a semiconductor wafer provided with bump electrodes, making the semiconductor wafer into singulated semiconductor chips by dicing, and then, flip chip connecting the semiconductor chips to a circuit substrate (see Patent reference 2) and an adhering film for using thereto were proposed. In this method, it is possible to make the adhering areas of the adhesive composition for semiconductor and of the semiconductor chip substantially equal and, compared to a case in which a liquid encapsulant is used, flowing out of the adhesive composition from the semiconductor chip is very little (see Patent references 3 and 4). However, the adhesive composition for semiconductor used in Patent references 3 and 4 are those composed of a phenoxy resin having fluorene skeleton, an epoxy resin, a micro-capsulated imidazole derivative epoxy compound and a filler, or those composed of an organic-solvent-soluble polyimide, an epoxy resin, a phenol resin and an inorganic filler. Since these contain a much amount of inorganic filler or micro capsule, its light transmittance is low and detection of alignment marks on semiconductor chip cannot be done, which is carried out when the dicing is carried out and when the flip chip bonding of semiconductor chip after dicing is carried out. Further, in case where an alignment is carried out based on a position detection of the bump electrode, instead of alignment marks, the position detection of the bump electrode is also difficult.
In case where the thickness of adhesive composition layer for semiconductor formed on the semiconductor chip is less than the thickness of the bump electrode, position detection of the bump electrode becomes possible, but since a bad connection is caused in case where the thickness of adhesive composition layer for semiconductor is less than the thickness of bump electrode, it can be used only when the thickness of adhesive composition layer for semiconductor and the thickness of bump electrode are substantially same. Further, since number of bump electrodes on semiconductor wafer is very large, it is very difficult to adjust the thickness of adhesive composition layer for semiconductor with every bump electrode height. Furthermore, there are various shapes as the bump electrode such as plate-like, cylindrical, hemispheric, mushroom-like, protuberant, and in those of hemispheric, mushroom-like and protuberant, in case where the thickness of adhesive composition layer for semiconductor and the thickness of bump electrode are same, since detectable area becomes small, detection becomes extremely difficult. Further, in other than those containing an inorganic filler or micro capsule, compositions having an island structure of several micron size due to a low compatibility between resins (so-called composition of sea-island structure), for example, in mixed systems of an epoxy resin and NBR (acrylonitrile-butadiene copolymer) or the like, a light transmittance becomes low and problems similar to the above-mentioned arise.
Furthermore, when a dicing is carried out after the liquid encapsulant described in Patent reference 1 is coated on the bump electrode surface side of the semiconductor wafer, several problems may occur such as a problem that a dicing dust is apt to stick to liquid encapsulant, that the liquid encapsulant sticks to wafer edge surface due to high flowability of liquid encapsulant or a problem of clogging of dicing blade, or a problem of roughening of film surface caused by water ejecting pressure. For that reason, it is difficult to industrially adopt the process that dicing is carried out after coating the liquid encapsulant described in Patent reference 1 on bump electrode surface side of the semiconductor wafer. Further, when the dicing is carried out after laminating adhesive composition for semiconductor described in Patent references 3 and 4 on surface of bump electrode of the semiconductor wafer, there are problems that dicing dust is apt to stick to the liquid encapsulant, that a delamination of the liquid encapsulant from the wafer, or a defect or crack of the liquid encapsulant is caused. Although the defect or crack of the liquid encapsulant can be improved to a certain extent by decreasing the speed of cutting, when the recent situation in which wafer diameter enlargement is going on is considered, decreasing of dicing speed becomes a factor of cost up. Furthermore, in the adhesive composition for semiconductor described in Patent reference 3, a phenoxy resin having a fluorene skeleton or an organic-solvent-soluble polyimide is used to add a heat-resistance, but it has not a sufficient heat resistance or insulating property as an adhesive composition to coat the semiconductor wafer provided with bump electrodes.
On the other hand, in Patent reference 5, a method of combining an epoxy resin excellent in compatibility with polyimide and an organic-solvent-soluble polyimide is disclosed. By applying this method, an adhesive sheet of a high light transmittance can be obtained. However, it has a very brittle property since a solid epoxy resin is used as the epoxy resin, and when dicing is carried out after laminating to semiconductor wafer provided with bump electrodes, delamination from the wafer, or defect or crack of the adhesive itself is caused.
Further, a method of mixing a solid epoxy resin which is solid at room temperature and an epoxy resin which is liquid at room temperature to give flexibility has been known (see Patent reference 6). However, when a dicing is carried out after forming an adhesive layer consisting of these resins on a semiconductor wafer provided with bump electrodes, there are problems of delamination of the adhesive composition for semiconductor from the wafer, or that a defect or crack of the adhesive composition for semiconductor occurs.
Furthermore, an adhesive sheet which contains a polyimide, an epoxy resin of 3 functional or more and a liquid epoxy resin is also disclosed (see Patent reference 7). However, when a flip chip assembly is carried out by using the adhesive sheet containing polyimide described in Patent reference 7, since water absorbability of this polyimide is high, the water stored by the absorption in the adhesive sheet evaporates rapidly by being heated at the time of mounting, and accordingly, the adhesive sheet foams, and problems arise such as that the adhesive strength between semiconductor chip and circuit substrate cannot sufficiently be obtained, or that the connection reliability becomes low.
Further, as organic-solvent-soluble polyimide, a polyimide having a reactive group such as phenolic hydroxyl group at main chain end of the polymer (see Patent reference 8) has been known.
[Patent reference 1] Specification of US2004/132888,A
[Patent reference 2] Specification of US2001/16372,A
[Patent reference 3] JP2004-315688,A (scope of claims)
[Patent reference 4] JP2004-319823,A (scope of claims)
[Patent reference 5] JP2003-192894,A (Claim 1)
[Patent reference 6] JP2004-146495,A (Claim 11, column 39)
[Patent reference 7] JP2004-292821,A (scope of claims, column 73)
[Patent reference 8] Specification of EP1630605,A
The present invention provides, in order to solve the above-mentioned problems, an adhesive composition for semiconductor which does not cause crack or delamination even when being flexed, which can be laminated to bump electrode side of semiconductor wafer provided with bump electrodes of a narrow pitch and a high pin count, which permits a high-speed cutting without a contamination with dicing dust and without a defect at the time of dicing, and which is excellent in detection of alignment marks at the times of dicing and flip chip assembly. And, this invention provides an adhesive composition for semiconductor which is possible to highly precisely metallic bond a highly precisely cut semiconductor chip to an electrode pad of circuit substrate via bumps, or by being able to achieve a stable electric conduction by contact between conductive materials, and by functioning as an adhesive which gives a shrinking stress between the semiconductor chip and the circuit substrate, which assists stable electric conduction by this metallic bonding between the electric conductive materials and functions to enhance reliability of the connection.